1. Field of the Invention
The present invention relates to a molding sheet material of a fiber reinforced thermoplastic resin used in hot stamping or high-speed compression molding, particularly to a molding sheet material suitable for use in the molding of an article having a relatively large thickness and a deeply drawn three-dimensional structure and suitable for use in the field where a mechanical strength is required. Further, the present invention relates to a toe puff for a shoe produced by molding the above-described molding sheet material, particularly to a toe puff for a safety shoe which can be applied to shoes, such as shoes and boots, to reinforce the structure of the shoe puff, thereby enhancing the safety of the shoes.
2. Description of the Prior Art
A molding sheet material of a fiber reinforced thermoplastic resin which has hitherto been used in hot stamping or high-speed compression molding comprises a fiber reinforced thermoplastic resin reinforced with a reinforcement such as a chopped strand mat, a filament mat or a nonwoven fabric, each used singly. In recent years, a sheet material for stamping molding reinforced with a unidirectional reinforcement consisting of doubled reinforcing fibers has also been developed.
In a toe puff of a safety shoe, a great importance has hitherto been attached to the strength of the upper of a shoe for the protection against the dropping of a heavy material, and only a shoe puff consisting of a steel has been put to practical use. Since, however, the steel toe puff has a large weight, there occurs a problem with the workability of a person wearing such shoes. For this reason, in recent years, a toe puff for a safety shoe consisting of a thermoplastic resin reinforced with a reinforcing filament, such as a glass fiber, has been proposed for the purpose of reducing the weight of the toe puff. For example, Japanese Utility Model Publication No. 42402/1986 proposes a toe puff for a safety shoe produced by subjecting a base material consisting of a glass filament composited with a thermoplastic resin matrix to heat molding under pressure, and Japanese Utility Model Publication No. 64304/1987 proposes a toe puff for a shoe produced by press molding, injection molding or the like through the use of a filament in the form of a cloth, a yarn, a braid, a mat or the like.
Molded articles produced from a molding sheet material reinforced with the conventional mat or nonwoven fabric, however, has a low strength, which renders the molded articles unsuitable for applications where a high strength is required. When the above-described sheet material is subjected to deep drawing, it is partially elongated to a large extent. In the excessively elongated portion, the reinforcement as well is elongated. This lowers the strength and reduces the thickness unfavorably. In this respect as well, the sheet material is unsuitable as a toe puff for a safety shoe. On the other hand, in the sheet material reinforced with a unidirectional reinforcement, it is a matter of course that the directionality occurs in the strength of the molded article, which renders such a sheet material unsuitable for the production of a molded article where a high strength is required independently of the directionality, such as a toe puff for a safety shoe.
When a woven fabric or a knitted web is used as a reinforcement for the molding sheet material, it is conceivable that the resultant article is satisfactory in respect of both the strength and the directionality. Since, however, the molding sheet material wherein the woven fabric or knitted web is used as the reinforcement is difficult to elongate and bend, when the sheet material is molded into a three-dimensional structure, wrinkling or creasing occurs in the bend, so that no good molding can be conducted. For this reason, at the present time, such a molding sheet material is not put to practical use.